Group 2, Group 7 & Periodicity - A Level Chemistry

OCR H432 · 3.1.2 · 3.1.3 · 3.1.4

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3.1.2(a) the outer shell s² electron configuration and the loss of these electrons in redox reactions to form 2+ ions 3.1.2(b) the relative reactivities of the Group 2 elements Mg → Ba shown by their redox reactions with:
(i) oxygen
(ii) water
(iii) dilute acids 3.1.2(c) the trend in reactivity in terms of the first and second ionisation energies of Group 2 elements down the group (see also 3.1.1 c) 3.1.2(d) the action of water on Group 2 oxides and the approximate pH of any resulting solutions, including the trend of increasing alkalinity 3.1.2(e) uses of some Group 2 compounds as bases, including equations, for example (but not limited to):
(i) Ca(OH)₂ in agriculture to neutralise acid soils
(ii) Mg(OH)₂ and CaCO₃ as ‘antacids’ in treating indigestion. 3.1.3(a) existence of halogens as diatomic molecules and explanation of the trend in the boiling points of Cl₂, Br₂ and I₂, in terms of induced dipole–dipole interactions (London forces) (see also 2.2.2 k) 3.1.3(b) the outer shell s²p⁵ electron configuration and the gaining of one electron in many redox reactions to form 1− ions 3.1.3(c) the trend in reactivity of the halogens Cl₂, Br₂ and I₂, illustrated by reaction with other halide ions 3.1.3(d) explanation of the trend in reactivity shown in (c), from the decreasing ease of forming 1− ions, in terms of attraction, atomic radius and electron shielding 3.1.3(e) explanation of the term disproportionation as oxidation and reduction of the same element, illustrated by:
(i) the reaction of chlorine with water as used in water treatment
(ii) the reaction of chlorine with cold, dilute aqueous sodium hydroxide, as used to form bleach
(iii) reactions analogous to those specified in (i) and (ii) 3.1.3(f) the benefits of chlorine use in water treatment (killing bacteria) contrasted with associated risks (e.g. hazards of toxic chlorine gas and possible risks from formation of chlorinated hydrocarbons) 3.1.3(g) the precipitation reactions, including ionic equations, of the aqueous anions Cl⁻, Br⁻ and I⁻ with aqueous silver ions, followed by aqueous ammonia, and their use as a test for different halide ions. 3.1.4(a) qualitative analysis of ions on a test-tube scale; processes and techniques needed to identify the following ions in an unknown compound:
(i) anions:
• CO₃²⁻, by reaction with H⁺(aq) forming CO₂(g) (see 2.1.4 c)
• SO₄²⁻, by precipitation with Ba²⁺(aq)
• Cl⁻, Br⁻, I⁻ (see 3.1.3 g)
(ii) cations: NH₄⁺, by reaction with warm NaOH(aq) forming NH₃.

Group 2, Group 7 & Periodicity

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